a. Field of Invention
This invention pertains to digital modems and more particularly to a digital modem using QAM type modulation and having automatic error correction.
b. Description of the Prior Art
While in analog communication exchange errors caused by various interferences due to external causes or channel distortions can be usually tolerated, in digital data communications such errors can have grave consequences and therefore great and painstaking efforts have to be made to minimize them. For example many modems are provided with automatic gain control (AGC) circuits which monitor the amplitude levels of the received signals and an output to the demodulator section of a receiver. The AGC gain is dynamically adjusted to try to maintain said output within a preselected amplitude range. However it was found that for relatively fast excursions of the received signals, these AGC circuits are ineffective.